Tilt variations of structures are measured frequently and notably in the case of measurement of geophysical deformations, more specifically seismic or volcanic deformations. Such measurements are also carried out to warn of the possible danger of collapse of buildings or a portion thereof or to monitor changes in the storage of fluids in geological storage sites and the migration of these fluids into the permeable layer. These measurements can also be used to monitor the horizontally of large industrial structures.
During an earthquake, in fault areas, the movement of geological faults occurs rapidly. Detection of these movements is easy. Between two earthquakes deformations exist but are very small and very slow. Now these deformations are linked to seismic activity and detection of these deformations is essential for understanding the mechanism of faults in the earth's crust. It is therefore necessary to use measuring instruments that are very stable and reliable in the long term, from several years to several centuries.
At present there are no commercially available devices that can be installed in an array and are capable of producing a high-resolution measurement that is stable in the long term. The devices known at present are generally bubble tiltmeters, pendulum tiltmeters. Such devices can be installed in bores and in arrays but prove unstable in the long term. Other known devices include hydrostatic tiltmeters associated with capacitive, magnetic or linear variable differential transformer (LVDT) induced current sensor type measuring systems. The latter can prove stable in the long term but have the disadvantage that they cannot be installed in bores and therefore in an array. Moreover, all of these devices use electronic components that are too close to the sensor, significantly reducing the long-term reliability of the device. All these devices enable quantification of the deformations based on the measured tilt variations.